Autosomal recessive pituitary dwarf mutats of the Ames and Snell- Bagg mouse strains have defective immune systems. This was demonstrated by progressive involution of immune tissue (espcially the thymus), low lymphocyte counts in blood, defective antibody responses and abnormalities of other immunologic parameters. These dwarf mice always developed a wasting syndrome at young age. Experimental evidence has indicated that the thymus-dependent immune system is deficient in dwarf mice as a direct consequence of a defective thymotropic pituitary influence on the thymus gland. I have also shown that the immunodeficiency can be prevented by prolonged nursing of dwarf mice with foster mother and also by injections of mouse milk in dwarf mice after the time of weaning. The hypothesis has been presented that a specific milk factor influences cellular immune function in dwarf mice and perhaps also of newborn animals in general. The proposed research is a continuation of the studies of various aspects of the immunodeficiency of dwarf mice. These studies will help us to gain insight into the endocrinologic relationship of the immune system, and in particular the role of the pituitary glnad. A major part of this project will deal with the study of the lymphopoietic milk factor, which prevents the immunodeficiency of dwarf mice and which may generally have an influence on the full development of cellular immune function of the newborn. Experiments have been designed to determine the effect of human and mouse milk on immune function as well as to isolate milk factor and study its mode of action. Thus far the immunologic aspects of milk have only dealt with the passive transfer of antibodies from the mother to the newborn. An association between milk and cellular immune function has never been mentioned, although cellular immunity plays a most important role in host defense against many infectious agents and in the control of malignant change. The studies of the effect of milk on cellular immune function will provide us a better understanding of the immunologic interactions between mother and offsping.